Opposed flow spinneret blanketer

ABSTRACT

A spinneret blanketer in which heated inert gas is passed through a spinning pack to two channels which direct opposed inert gas streams across the spinneret face. The channels are bounded on their upper side by the spinneret face and on the lower side by a spinneret retainer having a lip whose lower face forms an angle of less than 45* to the spinneret face. The lip serves to deflect the normally present current of upward flowing ambient air so that it flows at an angle of less than 45* to the spinneret face where it approaches the inert gas stream. Preferably, the opposed inert gas streams are of unequal velocities so that the streams will meet at a front remote from the filaments.

United States. Patent [191 Heckrotte et al.

[451 Sept. 25, 1973 OPPOSED FLOW SPINNERET BLANKETER [75] Inventors: Robert Sherwood lleckrotte; John Alexander Scott, both of Wilmington, Del.

[73] Assignee: E.-l. du Pont de Nemours and Company, Wilmington, Del.

[22] Filed: Apr. 24, 1972 [21] Appl. No.: 247,162

52 U.S. C1 264/237, 214/176 F [51 Int. Cl. B29c 25/00 [58] Field of Search 425/72; 264/176 F, 264/237 [56] I I References Cited UNITED STATES PATENTS 2,252,689 8/ 1941 Bradshaw 425/72 2,821,744 2/1958 Spohn et al..... 425/72 2,832,642 4/1958 Lennox 425/72 3,061,874 11/1962 Lees... 425/72 3,070,839 1/1963 Thompson 425/72 3,115,385 12/1963 Beck 425/72 Primary Examiner-Jay H. Woo Attorney-Howard P. West, Jr.

[ 5 7 ABSTRACT A spinneret blanketer in which heated inert gas is passed through a spinning pack to two channels which direct opposed inert gas streams across the spinneret face. The channels are bounded on their upper side by the spinneret face and on the lower side by a spinneret retainer having a lip whose lower face forms an angle of less than 45 to the spinneret face. The lip serves to deflect the normally present current of upward flowing ambient air so that it flows at an angle of less than 45 to the spinneret face where it approaches the inert gas stream. Preferably, the opposed inert gas streams are of unequal velocities so that the streams will meet at a front remote from the filaments.

2 Claims, 9 Drawing Figures OPPOSED FLOW SPINNERET BLANKETER BACKGROUND OF THE INVENTION The present invention relates to the production of synthetic filaments and particularly to a method and an apparatus in which the exposed face of a spinneret is blanketed with an inert gas.

In melt spinning operations, some of the fiber forming material tends to build up on the spinneret face around each extrusion orifice and oxidize into a hard deposit which eventually interrupts the spinning process. This has been partially avoided by directing inert gas across the spinneret face in an effort to exclude all oxygen. Shrouds or shields have been used to protect the inert gas from ambient air currents. Despite these measures, the ambient air is found to have a velocity component upward and generally normal to the face of the spinneret so that the air either displaces the inert gas or mixes with it, providing oxygen for degrading newly formed extrudate.

The upward flow of ambient air is induced in several ways. The movement of each spinning filament carries a boundary layer of gas downward and this pumping action of the filaments is frequently sufficient to induce a flow of ambient air upward toward the spinneret to replace the gas removed. The inert blanketing gas emerging'from a stream'forming gap creates a reduced pressure zone at the point of emergence which aspirates a flow of ambient air toward the spinneret face along the nearest lower face' of the spinneret retainer. If the inert gas flow velocity is raised in an attempt to provide more protection, more ambient gas is aspirated and the flow becomes more turbulent so that more oxygen mixes with the inert gas. In addition, quenching air which contacts the filaments is heated by such contact and becomes lighter than the surrounding air, thus forming upward convection currents, particularly on the side of the spinning filaments away from the source of quench air. The walls of the members surrounding the spinning filaments are frequently perpendicular to the spinneret face so that any ambient gas streams which contact such walls approach the inert gas blanketed zone next to the spinneret under conditions most likely to cause mixing of the air into the inert gas. Furthermore, if a thin layer of blanketing gas is unconfined so that spent blanketing gas exits laterally in the plane of the spinneret, more ambient air is allowed to approach the blanketed zone than in confined blankets and thus provide greater opportunity for mixing.

SUMMARY OF THE INVENTION The present invention is directed to methods and means for minimizing ambient air velocity components directed toward a spinneret blanketed with inert gas and preventing penetration of oxygen through the inert gasblanket to the spinneret face. It has now been found that in a process for the formation of filaments by extrusion of molten filament forming composition from a spinneret into a gaseous medium, the newly emergent portions of molten composition being subject to degra dation in the presence of ambient gases, currents of ambient air approaching said inert gas blanket next to a spinneret face may be prevented from penetrating the inert gas by guiding a generally rising current of ambient air which contacts a spinneret retainer adjacent to a melt spinning filament so that the ambient air current flows at an angle of less than 45 to the spinneret face where it approaches a stream of hot inert gas flowing parallel to and in contact with the spinneret face. Preferably, the ambient air current is directed parallel to the inert gas stream. Where two opposed inert gas streams are employed to blanket a rectangular spinneret, it has further been found that penetrating and mixing of ambient air with the inert gas is minimized if the opposed inert gas streams have velocities such that only one stream passes the filaments and the two streams meet along a front remote from the filaments. Where the filaments are centered between the sources of the opposed streams, the streams will have unequal velocities. An inert gas stream preferably has no discontinuities and low turbulence where it emerges from the stream forming region.

Apparatus for the formation of filaments by extrusion of molten filament forming composition from a spinneret into a gaseous medium comprises a spinneret and a retainer below the spinneret defining a gap between the spinneret and the retainer and means for supplying inert gas to the gap the retainer terminates in a lip at the point of its nearest approach to the spinning filaments. Preferably, the vertical dimension of the lip sep' arating the ambient gas from the inert gas at its point of closest approach to the spinning filaments is less than the vertical dimension of the slot and may be less than'0.07 inch. A distributionand metering system is also incorporated between the inert gas supply and the gap to produce uniform gas flow patterns.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial end elevational view of a spinning position, partly in cross section, showing apparatus and means for supplying heated blanketing fluid to a rectangular spinneret assembly of this invention.

FIG. 2 is a view of the spinneret assembly from below as indicated at X-X in FIG. 1.

FIG. 3 is an enlarged partial cross section of a spinneret and retainer of FIG. 1.

FIG. 4 is a plan view of a fluid distributor 45 of FIG. 3.

FIG. 5 is a cross section of distributor 45 taken along line Y-Y of FIG. 4 showing the relationship between distribution slots 46 in distributor 45 and fluid manifold 34 in retainer 14.

FIG. 6 is a cross-sectional view of a prior art rectangular pack and spinneret in which inert gas is introduced along both sides of the apparatus, showing inert gas and ambient air flow patterns.

FIG. 7 is a cross-sectional view of a rectangular pack and spinneret of the invention, similar to FIGS. 1 and 3, except showing both sources of inert gas and introducing inert gas at unequal velocities from opposite sides of the apparatus.

FIG. 8 is a cross section of a circular spinneret showing flow patterns when using the process and apparatus of the present invention.

FIG. 9 is a partial view of the circular spinneret of FIG. 8 as seen from below.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS In general, the process of the present invention may be utilized in a number of different apparatus configurations, the principal ones employing either a rectangular spinneret or a circular spinneret. The apparatus with the rectangular spinneret will be described first and in these embodiments the exposed face ofthe spinneret is substantially planar. However, curved or domed shapes for the spinneret are also contemplated, as in Heckrotte U. 8. Pat. No. 3,466,703.

Referring to FIGS. 1 and 2, spinning pack assembly 24 is supported within cavity 1 of heated block 2 by screw 3. Hot inert gas is supplied to pack 24 through passage 4, its total flow rate being governed by a metering orifice (not shown). Gasket is compressed by screw 3 and prevents leakage of inert gas at the joint between passage 4 and pack assembly 24. A similar gasket seals the polymer supply system (not shown). Within pack 24 the inert gas flow divides, part passing through passages 30, 31 and 32 into spinneret l1 and thence into spinneret retainer 14 and part passing through passages 30a, 31a and 320 into the opposite side of spinneret 11 and spinneret retainer 14a. The inert gas then flows along the lower surface of spinneret 11 from both retainers 14 and 14a toward polymeric filaments 15. The outer surface of block 2 is covered with insulation except for the bottom portion of cavity 1 which is open to a conventional quenching chimney 21 having a pair of parallel wings 22 and a source 23 of cool quenching air which flows generally horizontally to the left to be exhausted to the room beyond the edges of the chimney wings 22.

Referring particularly to FIG. 2, spinning pack assembly 24 has clearance within cavity 1 in a left and right driection of FIGS. 1 and 2 to allow for movement of the pack 24 during installation and removal under the influence of screw 3. Pack 24 fits closely, however, with walls 61 and 62 of cavity 1 so that the inert gas blanket is confined and can only leave the spinneret region in a downward direction.

Referring to the larger scale cross section, FIG. 3, situated between the lower face of the spinneret 11 and the upper face of the retainer 14 is a pair of thin plates comprising a metering plate 44 and a distribution plate 45, both of which are coextensive lengthwise (i.e., in a direction perpendicular to the plane of the drawing) with both the spinneret and the retainer. The retainer 14 has several parallel longitudinal grooves comprising a manifold passage 34, a dissipator passage 47 and a shallow slot 48, all of which terminate about 0.1 inch short of the respective ends of the retainer 14. Directly above the retainer 14 is the distribution plate 45 which has a single, large diameter aperture 49 (D diameter, 0.19 inch) above the manifold passage 34.

Surmounting the distribution plate 45 is the thin (0.010 inch) metering plate 44 which has a single metering orifice 43 of diameter D, smaller than D,; the orifice 43 is aligned with the aperture 49 in the plate 45 as well as with the aperture 33 in the lower face of the spinneret 11. The longitudinal edges of the plate 44 are bent 90 downward (i.e., away from the spinneret) along both longitudinal edges, on the one edge to engage a locating groove 52 in the retainer 14 and on the opposite edge to enter approximately the center of the dissipator passage 47 to a sufficient depth to act as a shroud around the right hand edge of the plate 45 and the exit portions of the slots 46 over the land 50. Slot 48 confronts and has a wall parallel to the lower face of the spinneret 11 forming a gap 36, the height A" of which is determined, in part, by the thicknesses of the plates 44 and 45. The gap 36 has a length L" in the direction of flow which is at least three times the height "A".

The lip 37 of the retainer 14, beneath the gap 36 comprises a thin member (thickness "T" greater than zero but equal to or less than 0.07 inch); the lower face 38 at its closest approach to the filaments is preferably planar, the projection of this face to its intersection with the spinneret face making an angle ofless than 45 with the spinneret face. Preferably, the lower face 38 is parallel to the spinneret face and must have a width W in the transverse direction (i.e., in the direction of flow of blanketing gas) of at least about 0.1 inch. The spinneret retainer 14 must, of course, be thick since it supports the spinneret by means of bolts (not shown); thus, since the lip 37 is thin, the left part of face 38, FIGS. 1 and 2, preferably merges tangentially into a curving face of concave, then convex shape known as a cyma curve. The magnitude of the radii of the cyma curve is relatively unimportant. The distance 8" between the edge of the lip 37 and the nearest filament 15 should be from about 0.05 to 0.3 inch, preferably about 0.2 inch. The open space across the spinneret lipto-lip should not exceed about six inches.

Referring to FIGS. 4 and 5, the distribution plate also has a comblike edge with a plurality N of slots 46 with a center-to-center spacing E, a width F and a length G, the thickness of the plate 45 being'designated as J, typical values being as follows:

N 56 slots E 0.21 inch P 0.032 inch G 0.19 inch J 0.018 inch In FIG. 5, it will be seen that the U-shaped ends of the slots 46 lie above the manifold passage 34 while the remainder of each slot lies'across the land 50 between the manifold passage 34 and the dissipator passage 47. The aggregate cross-sectional area of all the slots 46 (N X F X J), taken at right angles to the direction of fluid flow, should be less than the cross-sectional area of the manifold passage 34 in order to assure substantially equal distribution of the blanketing fluid from end-toend of the gap 36. In the example (above) the slots 46 have an area:

56 X 0.032 inches X 0.108 inches 0.034 sq. inch while the manifold passage 34 has an area:

0.22 inches X 0.31 inches 0.068 sq. inch The operation and benefits of the present process and apparatus may best be illustrated by comparison with the prior art. In a prior art rectangular spinneret assembly of FIG. 6, streams 54 and 54a of inert gas emerge from the gaps 36 and 36a and sweep across the face of the rectangular spinneret 11 through the region occupied by the newly emergent filaments 15 which divide the stream, slow it down and create turbulence. Currents of ambient air 53 pass between the filaments, are heated by the filaments and rise due to convection and filament pumping. Vertical wall 63 of the spinneret retainer directs part of air 53 vertically toward inert gas stream 54 and the spinneret face. This air mixes with the inert gas, enters the filament array and is available to oxidize the polymer. The pumping action of the filaments moves the mixture downward. Furthermore, the stream of inert gas 54a aspirates a current of ambient air 530 which follows the vertical wall 63a and mixes into stream 54a at its point of emergence.

In contradistinction, using the process of the present invention with a rectangular spinneret (as shown generally in FIG. 7) (or a rectangular array of filaments in a nonrectangular spinneret), two fluid streams 54 and 54a of unequal velocity emerge from gaps 36 and 36a, respectively. In this situation, the different velocities of the two streams are established as described below being determined, in part, by the location of the perimeter of the filament bundle relative to the end of. the lip 37 on each of the retainers 14. Referring now to the filaments on the extreme left side of the bundle, i.e., the ones nearest to the lower velocity stream 54, the velocities of the two fluid streams are proportioned so that they will abut each other and merge between these left side filaments and the end of the lip 37 generally in the region 55 denoted by the broken line. Rising currents of ambient air 56 encounter lower face 38 of lip 37 which turns them so that they approach inert gas streams 54 at an angle of less than 45 to the spinneret face and preferably parallel to it so as to reduce or eliminate mixing at the interface between inert gas and arr.

The supply of inert gas to one spinneret is first controlled by an orifice of 0.038 inch diameter (not shown) installed in passage 4, this size having been selected to provide a flow between 2.0 and 5.0 lb. per hour of dry steam at a supply pressure of about 70 psig and 290C. The relative sizes of the orifices 43 (FIG. 3) and 430 (on right side, not shown) of diameter D were selected to provide about twiceas great a flow rate from the right (or quench air supply side) as from the left (the operator's side), orifice 43 being 0.088 inch diameter and orifice 430 being 0.125. This flow ratio (in pounds per hour) may be in the order of 1.511 to a maximum of about 4:1. When the total flow rate is 4.5 lb. per hour, the divided fluid streams emerge from gaps 36, 36a (See FIG. 7) at velocities of 2.07 and 4.14 ft. per second, respectively. Since the right hand stream has the higher velocity, it persists as a discrete stream well across the face of the spinneret, e.g., in the order of 0.6 to 0.8 the width of the space, lip-to-lip; this stream gradually loses velocity so that at about the 0.8 point of the width, the velocity is about 50 percent of the starting velocity in the gap 36a and the stream then occupies about twice as much space vertically as when it left the gap. This slowing effect occurs in a smooth and orderly fashion with substantially no fluid turbulence and substantially no intermixing with quench air and other ambient gases except for a very slight mixing in an extremely thin layer on the side of the fluid stream remote from the spinneret face which is of no consequence.

The left hand fluid stream emerges from gap 36 at about half the velocity of the right hand stream and thus is not able to persist for as great a distance; in addition, it is directly opposed by the quench air flowing from the right. At about the 0.8 point of the width (measured from the right), the left fluid stream changes direction, thus at this point the right stream abuts the left stream and turns 90, the two flowing generally downward together substantially clear of the left hand filaments and thereafter mixing with the horizontally flowing quench air.

The maximum inert gas velocity in gaps 36 and 360 should be as low as practicable to minimize aspirating ambient air and to avoid turbulent mixing. The maximum velocity for providing a smooth, laminar flow should be in the order of 350 ft. pei minute (I07 m/min) and the Reynolds number should generally not be in excess of about 2,000. Within any given gap 36, the velocity should be uniform end-to-end of the gap within i 10 percent of the mean velocity.

FIGS. 8 and 9 depict a round spinneret with annular filament array employing the present invention in which a single generally circular spinneret retainer 14 has annular passager 34, etc. supplying inert gas to an annular gap 36, details of the inert gas distribution system being substantially the same as in the case of the rectangular spinneret as described above. Inert gas flows from annular gap 36 in a nonturbulent stream to converge centrally of the filament bundle in the region 59 which is clear of the locus of any individual filaments. Rising currents of ambient air 60 are deflected by lower surfaces 38 of lips 37 so that the air flows approximately parallel to the spinneret face where it joins the inert gas stream. Within the region 59 the fluid must, of course, change direction and flow generally downward; however, this occurs in a smooth and orderly fashion with minimum turbulence, maintaining an unbroken inert gas blanket next to the spinneret. The upward flow of ambient air in the middle of the filament array, as denoted by arrows 64, is deflected by the downward flow in region 59. In this embodiment, the flow rate of the blanketing fluid and the velocity ofthe fluid are kept somewhat lower than the maximums specified below for the rectangular spinneret to avoid turbulence particularly in the central region 59.

From the foregoing, it will be realized that according I to the present invention, the blanketing fluid streams,

in the regions of the newly emergent filaments, have no substantial discontinuities at the point of their emergence from the stream forming members. By discontinuities is meant abrupt divisions in a stream (i.e., by causing the stream flow around an island obstruction), intermixing with streams of unlike material, local reduction or thinning of a stream, turbulent regions, eddies and the like. As noted above, in situations in which fluid turbulence and/or mixing are unavoidable, the site of such turbulence is made remote from the filaments emerging from the spinneret 11 by a finite distance, e.g., at least several filament diameters or 0.1 inch or more.

What is claimed is:

1. In a process for melt-spinning filaments including the steps of extruding filaments through orifices in the face of a spinneret plate and introducing a flow of inert gas across and in contact with the face of the spinneret to exclude ambient air, said air having upward velocity components, said components being generally normal to the face of the spinneret, the improvement comprising: introducing said flow of inert gas as two opposed streams across the face of the spinneret, said streams having unequal velocities, only one of said opposed streams passing through said filaments, both streams meeting at a location remote from said filaments; and directing said upward velocity components to approach the inert gas flow in the same direction at an angle of less than 45 to the spinneret face.

2. The process as defined in claim 1, said components being directed to flow in the same direction and substantially parallel to said flow of inert gas. 

1. In a process for melt-spinning filaments including the steps of extruding filaments through orifices in the face of a spinneret plate and introducing a flow of inert gas across and in contact with the face of the spinneret to exclude ambient air, said air having upward velocity components, said components being generally normal to the face of the spinneret, the improvement comprising: introducing said flow of inert gas as two opposed streams across the face of the spinneret, said streams having unequal velocities, only one of said opposed streams passing through said filaments, both streams meeting at a location remote from said filaments; and directing said upward velocity components to approach the inert gas flow in the same direction at an angle of less than 45* to the spinneret face.
 2. The process as defined in claim 1, said components being directed to flow in the same direction and substantially parallel to said flow of inert gas. 